Quantitative Doping of Chlorine in Formamidinium Lead Trihalide (FAPbI₃−xClx) for Planar Heterojunction Perovskite Solar Cells

MACl, as additive to the standard FAPbI3 precursor solution, enables near-complete coverage perovskite film to stabilize the phase-pure black FAPbI3 annealing at 100 °C. A partial substitution of FACl for FAI in precursor solution is used to grow FA perovskites with controllable chlorine doped fraction, which improves the performance of the planar perovskite solar cell.